Occurrence and distribution of halophilic vibrios in subtropical coastal waters of Hong Kong

The summer occurrence and distribution of halophilic vibrios in the subtropical coastal waters of Hong Kong were investigated. The density of vibrios in six sample sites ranged from 90 to 6,700 per ml, which made up 0.41 to 40% of the total bacterial populations of these sample sites. The sucrose-positive vibrios were found to be much more common (88% of total vibrios) than the sucrose-negative ones. A total of 48 strains belonging to six Vibrio species were fully characterized. Among these, Vibrio alginolyticus was the most frequently isolated, followed by V. parahaemolyticus, V. harveyi, V. vulnificus, V. campbellii, and V. fluvialis. The finding that eight of the nine strains of V. harveyi showed a positive Kanagawa reaction warrants further study.     

Occurrence of potentially pathogenic vibrios and related environmental factors in Songkhla Lake, Thailand

Vibrios are halophilic bacteria that are ubiquitous in marine environments. Their occurrence in tropical lakes has rarely been investigated. In this study, the predominance and diversity of Vibrio spp. was investigated over a 12-month period in a coastal lagoon, Songkhla Lake, in southern Thailand. Water samples were collected at 2 stations in the estuary near Yor Island in Songkhla Lake. The predominant vibrios were detected by a culture-based method, using thiosulfate-citrate-bile salt-sucrose agar and CHROMagar Vibrio. The diversity of Vibrio spp. was evaluated using denaturant density gradient electrophoresis (DGGE). The highest numbers of total vibrios and Vibrio parahaemolyticus in both areas were observed during the summer. There was no significant correlation between the numbers of vibrios, including V. parahaemolyticus, and either the water temperature or plankton density. Variations in Vibrio species were observed with changes in salinity. Vibrio parahaemolyticus and V. cholerae non-O1/non-O139 were detected during the rainy season when the salinity dropped to nearly 0 parts per thousand. In both areas, V. alginolyticus was the most prominent species detected by the culture method, whereas Vibrio parahaemolyticus was detected by DGGE, every month. Other Vibrio spp. of potential public health concern were also detected by the culture method; they included V. vulnificus , V. fluvialis , and V. mimicus .     

Occurrence and distribution of halophilic vibrios in subtropical coastal waters of Hong Kong.

The summer occurrence and distribution of halophilic vibrios in the subtropical coastal waters of Hong Kong were investigated. The density of vibrios in six sample sites ranged from 90 to 6,700 per ml, which made up 0.41 to 40% of the total bacterial populations of these sample sites. The sucrose-positive vibrios were found to be much more common (88% of total vibrios) than the sucrose-negative ones. A total of 48 strains belonging to six Vibrio species were fully characterized. Among these, Vibrio alginolyticus was the most frequently isolated, followed by V. parahaemolyticus, V. harveyi, V. vulnificus, V. campbellii, and V. fluvialis. The finding that eight of the nine strains of V. harveyi showed a positive Kanagawa reaction warrants further study.     

Potentially pathogenic vibrios in brackish waters and mussels

Water and mussel samples were collected from two brackish lakes, used as mussel farms, at different times of the year, for the quantitative analysis of Vibrio spp. and for the isolation of potentially pathogenic species. The isolates underwent cultural and biochemical tests selected for rapid identification. Glucose oxidizing-fermenting and O/129 sensitive strains were distinguished on the basis of the following tests: sucrose and cellobiose utilization, sulphatase activity and polymyxin B resistance performed, respectively, on TCBS, CPC and SPS media. Responses to the presence of beta-galactosidase, salt requirement and growth on triple sugar iron medium were also added. A total of 125 from 152 isolates were referred to the species Vibrio fluvialis (55 strains), V. alginolyticus (40), V. parahaemolyticus (11), V. vulnificus (10) and V. mimicus (9). The remaining 27 isolates were not identified. The isolation of potentially pathogenic vibrios from cultivated mussels is a risk for health of people consuming raw seafood. Therefore, a long-term monitoring programme should also include the search for these bacterial species.     

常见致病性弧菌检测的研究进展

弧菌属是一类自然存在于海洋和海产品中的微生物。随着经济的发展,海产养殖业的繁荣及现代检测技术的出现,弧菌对人类健康及海产养殖业的危害也日益受到人们的广泛关注。本研究详细介绍了常见致病性弧菌的检测方法,并对常规分离鉴定方法、免疫学方法和分子生物学方法进行了综述,期望能为相关弧菌感染的诊断与预防提供新思路、新方法。     

Differential detection of vibrios pathogenic to shrimp by multiplex PCR

The research was focused on the multiplex polymerase chain reaction (PCR) differential detection of shrimp pathogens Vibrio harveyi, Vibrio campbellii and isolates from a variant strain of Vibrio (referred to as Philippine Vibrio isolates in this study) exhibiting characteristics distinct from these two species. Sequence alignment of the hemolysin gene from type strains Vibrio harveyi (NBRC 15634) and Vibrio campbellii (NBRC 15631), as well as 10 variant Philippine Vibrio isolates, was performed in order to design a set of hemolysin-targeted primers for the specific detection of the Philippine Vibrio isolates. Primer PNhemo amplified a 320-bp hemolysin gene fragment of the Philippine Vibrio isolates in PCR using 65 degrees C annealing temperature, but did not amplify the target gene fragment in type strains V. harveyi and V. campbellii. Another new primer (VcatoxR) targeting the toxR gene was designed for the specific detection of type strain V. campbellii under stringent 65 degrees C annealing temperature. PCR using VcatoxR primer resulted in the specific amplification of a 245-bp V. campbellii toxR fragment. The simultaneous use of three primer sets in PCR, including PNhemo and VcatoxR (the two new primers designed in this study), and a primer VhtoxR (previously reported for the specific detection of V. harveyi), resulted in differential profiles with 390-bp, 245-bp, and 320-bp amplicons for V. harveyi, V. campbellii, and variant Philippine Vibrio isolates, respectively. Presence of all three types of Vibrio shrimp pathogens in the sample could be detected with a multiplex PCR profile containing all the expected size amplicons.     

Power plays: iron transport and energy transduction in pathogenic vibrios

The Vibrios are a unique group of bacteria inhabiting a vast array of aquatic environments. Many Vibrio species are capable of infecting a wide assortment of hosts. Some of these species include V. parahaemolyticus, V. alginolyticus, V. vulnificus, V. anguillarum, and V. cholerae. The ability of these organisms to utilize iron is essential in establishing both an infection in their hosts as well as surviving in the environment. Bacteria are able to sequester iron through the secretion of low molecular weight iron chelators termed siderophores. The iron-siderophore complexes are bound by specific outer membrane receptors and are brought through both the outer and inner membranes of the cell. The energy needed to drive this active transport is achieved through the TonB energy transduction system. When first elucidated in E. coli, the TonB system was shown to be a three protein complex consisting of TonB, ExbB and ExbD. Most Vibrio species carry two TonB systems. The second TonB system includes a fourth protein; TtpC, which is essential for TonB2 mediated iron transport. Some Vibrio species have been shown to carry a third TonB system that also includes a TtpC protein.     

A comparison of three methods for assaying hydrophobicity of pathogenic vibrios

The surface hydrophobicity of strains of Vibrio alginolyticus, V. carchariae, V. damsela, V. harveyi and V. vulnificus , isolated from either diseased cultured grouper ( Epinephelus malabaricus ) or penaeids ( Penaeus monodon and P. japonicus ) was determined using three different methods:the salt aggregation test (SAT), bacterial adhesion to hydrocarbons test (BATH), and adherence to nitrocellulose filters test (NCF). The results obtained indicate that all the strains tested showed some degree of hydrophobicity with the type strain of V. harveyi (ATCC 25919) showing strong hydrophobic properties in all the methods. The SAT method used in the present study was modified to a microtitre tray test, an easier test to read than the conventional in glass slide methodology. All the 13 test strains were positive in the BATH test when n -octane was used as the solvent, but only one strain was positive when n -hexadecane was used as the solvent. It is suggested that this method using n -octane as solvent is suitable for assaying the hydrophobicity of pathogenic vibrios isolated from diseased aquatic animals.     

Molecular and genetic characterization of the TonB2-cluster TtpC protein in pathogenic vibrios

TtpC is a fourth required protein in the TonB2 energy transduction system in Vibrio anguillarum. TtpC is necessary for iron transport mediated by the TonB2 system and is highly conserved in all pathogenic vibrio species studied to date as well as several marine organisms. We show here that the TtpC proteins from selected pathogenic vibrio species can function with the TonB2 system of V. anguillarum to allow iron transport mediated by a chimeric TonB2 system where the native ExbB2, ExbD2 and TonB2 function with an episomally expressed TtpC in trans from a different species. The discovery that inter-species complementation occurs can be used to identify the functional regions of the TtpC proteins and will lead to an investigation of the mechanism of interaction between the TtpC protein and other members of the TonB2 system.     

First isolation of Shiga toxin 1d producing Escherichia coli variant strains in shellfish from coastal areas in France

AIMS: This study was carried out to evaluate the presence of Shiga toxin-producing Escherichia coli (STEC) and E. coli O157:H7 in shellfish from French coastal environments. METHODS AND RESULTS: Shellfish were collected in six growing areas or natural beds (B category) and nonfarming areas (D category) from July 2002 to August 2004. PCR detection of stx genes was performed on homogenized whole shellfish and digestive gland tissues enrichments. STEC strains were detected by colony DNA hybridization using a stx-specific gene probe and E. coli O157 strains were additionally searched by immunomagnetic separation with O157-specific magnetic beads. Stx genes were detected in 40 of 144 (27.8%) sample enrichments from mussels, oysters or cockles, 32 of 130 enrichments (24.6%) were from B-category areas and eight of 14 (57.1%) from the D-category area. Five strains carrying stx(1) or stx(1d) genes and one stx negative, eae and ehxA positive E. coli O157:H7 were isolated from six of 40 stx-positive enrichments. No relation was found between the total E. coli counts in shellfish and the presence of STEC strains in the samples. CONCLUSIONS: The STEC strains of different serotypes and stx types are present in shellfish from French coastal environments. It is the first isolation of STEC stx1d strains in France. SIGNIFICANCE AND IMPACT OF THE STUDY: Shellfish collected in coastal environments can serve as a vehicle for STEC transmission.     

Occurrence ofAlexandrium cohorticula in Japanese coastal water

Two clones ofAlexandrium cohorticula were isolated at Aburatsubo, Sagami Bay, Japan. Cultured cells of both contained high amounts of paralytic shellfish toxins. The toxicity of these isolates was comparable with that of highly toxic Thai clones. No significant difference in toxin components or their proportions was observed between Japanese and Thai strains. The optimum growth temperature of both strains was around 25 °C. Japanese strains survived at 15 °C, whereas Thai strains did not; the latter grew faster than the former at 30 °C.     

Occurrence and infective potential of the endophyte ofHippophaë rhamnoides L. ssp.rhamnoides in coastal sand-dune areas

Summary The infective potential (IP) of nodule homogenates from field-grownHippophaë rhamnoides L. ssp.rhamnoides was determined by counting the number of nodules formed on test plants after inoculation with various dilutions of the homogenates. The IP was almost constant,i.e. 10⁵ to 10⁶ per gram of fresh nodule material. Methods to store nodule material without loss of IP were tested. The IP of air-dried nodule powders stored at 6°C hardly decreased during a period of more than a year.Data are presented on the IP of soil samples from sites representing various stages of dune formation. BeforeH. rhamnoides appeared, the IP was low: 1 to 36 nodules were formed on test plants per kg of soil. This low IP was due to low numbers of infective endophyte particles in these soils. During the succession of theH. rhamnoides scrub, the IP of the soil increased, due to the increase in the number of endophyte particles in the soil. Gradually, however, nodulation was limited by other environmental factors. The nature of these factors is discussed.     

Distribution of pathogenic vibrios and other bacteria in imported frozen shrimps and their decontamination by gamma-irradiation

The distribution of pathogenic vibrios and other bacteria in eight samples of imported frozen shrimps and the effect of irradiation on these bacteria were investigated. Total aerobic bacteria were at 2×10⁴ to 4×10⁶/g. Coliforms consisted mainly ofEnterobacter. No salmonella were detected. A total of 66 isolates, includingVibrio parahaemolyticus, V. mimicus, V. alginolyticus, V. vulnificus, V. fluvialis and a few ofListeria monocytogenes, were obtained. The gamma-radiation dose needed to reduce by 10^–4 the number of vibrio isolates andAeromonas hydrophila was about 3 kGy in frozen shrimps, whereas about 3.5 kGy was required forL. monocytogenes.     

Nature management in coastal areas of Western Europe

The general environmental characteristics of West European coastal dunes and those of salt marshes are outlined. It is pointed out that the dynamical character of the dune system with its interaction between plants and sand in building and degeneration phases has been known for a much longer period of time than generally believed.As to the salt marshes the special significance is discussed of ungrazed marshes; the majority of the marshes having been under a grazing regime for a long time is elucidated.The distinction between internal management is mentioned, i.e. the measures taken to maintain or improve the qualities of an area, versus external management, i.e. the measures to prevent or counteract negative influences from outside the area.Nomenclature follows Heukels & Van Ooststroom (1977).